Since their initial development, the demand for plastics and polymers has continued to increase by leaps and bounds. For instance, in 1989 fifty-eight (58) billion pounds of plastics were manufactured for sale and use in the United States alone. In fact, it is projected that the demand for plastics will reach 76 billion pounds by the turn of the century.
With the continued increase in production and use of plastics, recent focus has turned to processes for recycling the plastics after they have been used for two important reasons. First, manufacturing plastics and polymers requires the use of precious natural resources which are lost if the polymers and plastics are subsequently disposed of.
Another important reason to recycle plastics is the fact that plastics and polymers are virtually non-biodegradable. Consequently, if plastics are disposed of into the environment by, for instance, being placed into a landfill, the plastics will not be broken down by soil organisms, but instead will physically and chemically degrade and slowly release their chemical contents into the soil. Besides taking up valuable landfill space, the environmental concerns associated with waste plastics has prompted a need for further development of polymer recycling strategies.
In order to effectively recycle most polymeric materials, however, the polymers must be separated and isolated from other materials with which they are typically found. For instance, products made with plastics often contain other materials, such as wood, paper, metals, glass, other polymers and various other materials. Unfortunately, once the polymers are commingled with other materials, recycling becomes significantly more complex and oftentimes becomes more expensive than landfill disposal and production of new products from virgin materials. Clearly, a need exists for an economical process adapted to recycle polymers contained in a mixture of different materials.
In the past, others have attempted to separate components from a multi-component system. For instance, in U.S. Pat. No. 4,714,526 to Pennisi, et al. a supercritical fluid extraction method for multi-component systems is disclosed. Pennisi et al., which is incorporated in its entirety by reference into the present application, is directed to a process for extracting pure components from a multi-component system by effecting a change in temperature at a pressure between the cross-over pressure points of the various components of the system.
U.S. Pat. No. 5,233,021 to Sikorski, which is also incorporated in its entirety by reference into the present application, is directed to recycling polymeric materials from carpets and other multi-component structures by means of supercritical fluid extraction. In Sikorski, the method includes extracting pure components from a multi-component structure by dissolving each component at an appropriate temperature and pressure in a super-critical fluid and then varying the temperature and/or pressure to extract particular components in sequence.
Various objects, features and advantages of the present invention, however, remain absent from the prior art as will be made apparent from the following detailed description.